Tag Archives: codes

In this series of blog posts, Peter Sutton, PhD candidate researching the post-war history of technology and industrial relations in the British Postal Service, offers some reflections on the history of the modern postcode. The significance of the postcode and its origins in the post-1945 era are considered followed by some archival examples tracing different aspects of its design along its journey from a specialised engineering concept to a universally recognised geographical referencing tool.

Royal Mail poster Poster relating to service standards (1983)

In some ways the postcode is simple, an intentional characteristic that was given priority during its design in the post-war era. It needed to be quickly understood by postmen and easily remembered by the public. Its function as an abbreviator of addresses made it simple almost by definition. Equally, the business strategy behind the postcode project was at its core straightforward. In 1968 a manual sorting system prevailed in which, it was estimated, letters were sorted on average 3.2 times during their journey. A letter finding itself on a more tortuous routing might be handled five or six times before delivery. With almost 30 million letters handled at the sorting frame every working day, and as wages rose steadily in real terms in the post-war era, this was an increasingly expensive arrangement. After a string of successful trials in the 50s and 60s, sorting machines capable of “reading” a series of phosphor dots offered a partial solution. If a letter, upon entering the system, could first be marked with the machine readable dots containing sorting instructions then, officials at GPO Headquarters reasoned, all subsequent stages of sorting could be automated. In this scenario, human labour in the sorting process would be mostly confined to making an initial imprint on each envelope by a human operator reading the postcode at a “coding desk” and punching the information into a keyboard. Subsequent re-sorting could then be done by machine, eliminating much duplication of effort. The modern postcode, from this perspective, began life as a crucial component of what was hoped would one day become an all-encompassing system of integrated, automated sorting offices equipped with “robot sorters”.

If the underlying economics of the postcode are simple, the course of its design was not. This was a long-term and highly complex process which encompassed, among other things, the design of a binary machine language, basic research in chemistry, the mathematics of code theory, field trials in which sorting staff and psychologists had their input, and considerable research into the needs of businesses. The likely response of the public was analysed as were many elements of the postal service itself and the entire effort was also seen in an international context as an interest in code-sorting was taken up in Europe, America and Japan. Reflecting on the origins of the code, the PO explained during a 1976 parliamentary inquiry that strict parameters were established upon its design in the 1950s. The public needed something memorable and uniform and compatible with the old city district codes. Operationally, the code needed flexibility to accommodate variations and ad hoc revisions to circulation and delivery, and would have to form two parts reflecting the outward and inward phases of sorting. (Outward sorting directs mail to a different city or region, while inward sorting directs mail to a particular address.) The characteristics required of the code therefore had to mesh with the demands of various economic and psychological aspects of letter writing. This was not forgotten by Post Office officials when asked to reflect on the origins of the code during a 1970s Parliamentary Inquiry into the Postal Service. “This financial requirement” they remembered, “was a major factor in determining the type of equipment developed which affected the shape of the postcode. For example, the method envisaged for imprinting the codes in machine language was by means of an operator using a keyboard; and there was a limit to the capacity of the code ‘translator’ device [the “brain” of a mechanised sorting suite] that could be developed at economic cost.” (Cmnd. 6954, Appendix to the Carter Report (Post Office Review), 1977.)

Think, therefore, of your own postcode. As I have mentioned, it will have two parts. There will be a maximum of seven characters. The first part – the “outward” part – will specify a district within your wider mail delivery area. (For instance a house in York’s third delivery district becomes “YO3”.) This part was designed for long-term flexibility in an evolving mail circulation system and might have three or four characters. However the second part – the “inward” part – is a standardised allocation allowing for local, computerised delivery scheduling. It will have one numeral followed by two alpha characters, representing the sub-district, street and group of houses for your address. All of these features were deliberately chosen and could have been different but for historic decisions taken in light of the geography, transport distribution and population density of 1960s Britain. This, by the way, is one reason why Australian, Japanese and American postcodes all differ in their format. All were created for the same simple purpose of making addresses easier to read by machines. But equally, for each, design requirements and restrictions have differed from country to country in quite complex ways.

Poster promoting postcode usage (c. 1980)

This and the previous post have very briefly outlined some of the general principals and historic background which have helped shape the design of modern postcodes. In the next post we go back to the 1950s to look a bit closer at the early history of sorting machines and how engineers helped create the code.